(1) Field of the Invention
The present invention relates generally to the field of heat exchanging and dissipation devices. Specifically, the present invention relates to the field of heat exchanging and dissipation devices particularly applied to reduce the heat content of a solid state electronic device, such as a semiconductor chip.
(2) Prior Art
Since the advent of solid state electronics and semiconductor devices (i.e., "chips"), there has been a great demand for reducing the size of such devices while increasing their complexity and power consumption. The resultant commercially produced electronic devices suffer from substantial heat production and power consumption due to the large number of transistors packed very densely within the chip package. In may cases, the actual heat radiation of the semiconductor device will damage or destroy the operation of the device if the heat is not rapidly exchanged with the outer environment. Due to the great demand for more powerful computer systems at reduced size and cost, power consumption and heat production of semiconductor devices are increasing in great proportion. For instance, it is not uncommon for semiconductors devices to require from 10 to 50 watts of power for normal operation. Such high power requirements also bring substantial heat consumption and radiation characteristics for such devices. Therefore, there is a demand for efficient heat exchanging devices that are applicable within the size, weight, and power requirements of solid state devices.
In the past there have been a number of prior art devices aimed at dissipating and exchanging the heat produced by solid state semiconductor devices. Once such prior art design is illustrated with reference to FIG. 1(A). This device 18 is a solid piece of uniform metal, such aluminum or steel. The plate 16 is machined such that it contains a number of heat radiating surfaces or finned plates 14. The heat exchanging device 18 also may have a support or base 10 which acts as an alternative heat radiation surface. The heat producing element, i.e., the semiconductor device, is placed onto the heat location 12 (approximately 1 inch by 1 inch in area). Using basic heat transfer characteristics of the metal plate 18, the heat generated at 12 is exchanged between the metal and the environment surrounding the plate over the surface areas of the exposed metal.
The type of heat exchange device as illustrated in FIG. 1(A) is not entirely advantageous because a normal metal plate does not provide a uniform heat distribution throughout the surfaces of the exposed metal due to the thermal resistance of the metal plate. In fact, the heat content or distribution of the plate drops off very quickly for surfaces a short distance from the heat source 12. Without uniform heat distribution across the radiation surfaces, the efficiency of this type of heat exchanger 18 is poor. In addition, to achieve meaningful heat exchanging capabilities, the heat exchanger of this type must be relatively large. According to FIG. 1(A), it can be seen that heat exchanger plate 18 is three to four times larger in dimension then the heat surface 12 which is representative of the relative size of the semiconductor chip. Such large size requirements may be acceptable for desktop computer systems. However, for any computer system having small size requirements such as portable, pen-based and laptop computer systems, such a large heat exchanging plate 18 would simply not be acceptable within their design specifications. What is needed, therefore, is a heat exchanging device that provides uniform heat distribution across the surfaces of the heat exchanging device as well as a device that will accommodate most size requirements of computer systems. The present invention offers such advantageous capabilities.
A second prior art heat exchanger device 20 is illustrated with reference to FIG. 1(B). Such a system 20 includes a heat generating device 22, such as a semiconductor device, and a heat radiator 24 that is in thermal contact with the heat generator 22. A coolant liquid is circulated through predetermined channels 25 of the heat radiator 24 such that a liquid path is formed. The coolant liquid collects heat exchanged from the source 22 as it flows through the heat radiator 24 and is pumped via pump 26 to a cooling unit or condenser 28. The condenser cools the liquid from pump 26, draws the heat from the liquid, and then recirculates the liquid back to the heat radiator 24 via flow channel 30 and the pump 26. It is appreciated that the condenser 28 may be implemented as a chamber having specialized heat radiation surfaces, such as metal plate 18 as discussed above. Further, the condenser may also be coupled thermally with a cool stream of secondary coolant liquid or air current which contributes to the cooling process. Such prior art devices as discussed above used to cool solid state devices are disclosed within U.S. Pat. No. 4,450,472 (dated May 22, 1984) and U.S. Pat. No. 4,573,067 (dated Feb. 25, 1986) both entitled, Method and Means for Improved Heat Removal in Compact Semiconductor Integrated Circuits, by D. B. Tuckerman as well as U.S. Pat. No. 4,109,707 issued on Aug. 29, 1978 to E. A. Wilson, entitled, Fluid Cooling Systems for Electronic Systems.
The above prior art cooling system is not entirely advantageous in the area of semiconductor device cooling for a number of important reasons. Size considerations within a computer system demand that the heat exchanger system be small. The above prior art system does not operate within tight space requirements of a computer system or other electronic device because of the various system components required, such as the pump 26, the circulation channels and the condenser 28. These devices simply require an excessive amount of space and are expensive to miniaturize. Further, within such a system there is a good likelihood of spillage and leakage of the coolant liquid from the closed loop system which can either cause the heat exchanger system 20 to malfunction or cause the computer system to malfunction. In addition, such systems do not allow easy repair and maintenance for the semiconductor device (i.e., the heat generator 22). This is the case because the heat radiator 24 is usually adhesively attached to the semiconductor device to provide a proper thermal couple. In order to remove the device for repair or upgrade, the coolant channels 30 must be separated from the heat radiator. This may cause leakage or spillage of the liquid from the closed loop system and requires reinjection of the coolant after the chip is replaced which is another maintenance expense associated with this prior art system.
Another drawback of such a system 20 is that the pump 26 and other coolant circulation devices are active devices and require power for operation. Such power may not be available in reduced power systems, such as portables and laptops. Also, these prior art systems 20 tend to be complicated in design and operation, requiring a condenser, pump, radiator, liquid channels, etc. The complexity tends to increase the cost of such system and also increases the system failure rate. As a result, what is needed is a heat exchanger that does not require any external pump or external condenser unit or external heat channels that may rupture or leak coolant or that require external power supply to provide coolant circulation. Further, it would be advantageous to provide a heat exchanger system that does not utilize active devices and that allows easy modification and access to the attached semiconductor device. The present invention provides such functionality.
With reference to FIG. 1(C), another prior art design 32 is illustrated. This prior design 32 utilizes a fan 38 to constantly circulate air over the solid state device 36. The air flow 40 will carry away heat radiated from the chip 36. This prior design 32 suffers from the same size requirements of most computer and electronic systems in that the fan typically requires too much room within the system. Further, fans are mechanical and have an inherent failure rate that may not be acceptable for an electronic system. Also, some portable computer systems may not have the space within the chassis to provide a clear air flow path. In addition, the fan 38 is an active device and requires power for operation, such as the pump of the other prior system 20. Therefore, what is needed is a heat exchanger system that does not require external power for operation and is reliable with a low failure rate. The present invention offers such capabilities.
Another prior system, disclosed in U.S. Pat. No. 4,975,803 issued Dec. 4, 1990 to R. E. Niggeman and entitled Cold Plane System for Cooling Electronic Circuit Components, utilizes a fluid filled chamber that is thermally coupled to the semiconductor device. However such a system exchanges heat based on movement of liquid vapor of a low boiling point liquid coolant. It would be advantageous to provide a system that exchanged heat based primarily on movement of a high boiling point liquid coolant that remains in liquid form at the operational temperatures of the target semiconductor device. This is desired because these coolants in liquid form operate more effectively within such a heat exchanger system and act to transfer more heat to the surface of the heat exchanger more efficiently. The present invention provides such an advantageous system.